Sewing machine for forming intermittently locked stitches



Jan. 20, 1970 5, HAMLETT 3,490,401

SEWING MACHINE FOR FORMING INTERMITTENTLY LOCKED STITCHES Filed Sept. 19, 1967 2 Sheets-Sheet 1 mmmLmmm m INVENTOR. SIO/I/Ey J )V4Md577' 1970 s. J. HAMLETT 3,490,401

SEWING MACHINE FOR FORMING INTERMITTENTLY LOCKED STITCHES Filed Sept. 19, 196'? 2 Sheets-Sheet B United States Patent C) 3,490,401 SEWING MACHINE FOR FORMING INTERMIT- TENTLY LOCKED STITCHES Sidney J. Hamlett, Parma, Ohio, assignor to White Consolidated Industries, Inc., Cleveland, Ohio Filed Sept. 19, 1967, Ser. No. 668,886 Int. Cl. D05b 3/02 US. Cl. 112159 8 Claims ABSTRACT OF THE DISCLOSURE A zig zag stitch sewing machine wherein the needle assembly and the bobbin and loop forming mechanism are shifted laterally of the bed plate in timed relationship to one another to form a stitch. A link is provided in the shift drive arrangement for the bobbin and loop forming mechanisms which can be selectively varied in length both to space the shuttle hook of the bobbin and loop forming mechanism away from the needle a suflicient distance to prevent the formation of an interlocked stitch and to move the shuttle hook adjacent to the needle to allow the formation of an interlocked stitch at intermittent times.

The present invention relates generally to sewing machines and more particularly to household type zig zag sewing machines of the type in which the loop forming mechanism oscillates about a horizontal axis parallel to the plane of the zig zag movement. In sewing machines of this type known as the side facing bobbin type the entire loop forming mechanism is shifted in timed rela tionship to the zig zag movement of the needle to provide the necessary precise positioning between the needle and the shuttle hook required for proper stitch formation. This type of machine is therefore distinguished from other types of machines such as the top bobbin type in which the loop forming mechanism rotates about a vertical axis or about an axis perpendicular to the movement of the needle in the front facing bobbin type.

Sewing machines of the side facing bobbin type are widely used because this type of construction is generally satisfactory for most purposes and can be manufactured at lower cost than either the top bobbin or front facing bobbin types, since both these latter designs require angled gear drives between the actuating shaft and the loop forming mechanism. With the side facing bobbin arrangement, the loop forming mechanism is mounted directly on the actuating shaft and a simple link arrangement is used to shift the loop forming mechanism along the axis of the actuating shaft in timed relationship with the zig zag movement of the needle so as to insure precise positioning between the needle and the loop taking mechanism at all times.

However, the side facing bobbin type sewing machine has heretofore suffered from certain limitations as compared to the other types of sewing machines. One of these limitations is that it has not heretofore been possible to produce a suitable basting type stitch With this machine. A basting stitch, that is, a stitch which is made for only temporary purposes, such as for holding pieces of cloth in a fixed relationship during the fitting of the garment, is widely used and a stitch for this purpose can be formed on both the top bobbin and front facing bobbin type machines. In the case of the top bobbin machine, an arrangement eliminating the bobbin and bobbin thread can be employed so that the machine can sew a chain stitch rather than the usual lock stitch, and this chain can be sewn with a rather long stitch spacing. In such case when it is desired to remove these stitches, it is only necessary to take hold of the free thread and pull it so that the entire series of stitches, not being locked, will unravel from the material and the thread will be completely removed.

In the front facing bobbin type machine, it has been possible to produce a basting type stitch which while being of the lock stitch type utilizing both the needle thread and the bobbin thread, is still of a type that can be easily removed. This is accomplished by using a special short needle and zig zag cam arrangement so that in one of the extreme zig zag positions, the needle, being shorter than the usual length does not form a loop beneath the fabric in a position where the shuttle hook can engage the loop, while still allowing such action to take place in the other extreme position of the zig zag movement. The zig zag cam or other controlling mechanism then proportions the needle reciprocations between these two positions so as to selectively allow a lesser number of lock stitches to be formed for a given number of needle reciprocations. With this arrangement a lock stitch is formed having an effectively greater stitch length than that determined by the normal stitch length setting of the fabric feed. However, such an arrangement cannot be used with the side facing bobbin because the needle loop and the shuttle hook always remain in the same relative position.

Therefore, it is a principal object of this invention to provide a novel side facing bobbin type zig zag sewing machine capable of producing basting type stitches.

It is another object of this invention to provide a novel zig zag sewing machine of the side facing bobbin type in which a pattern mechanism can be utilized so as to produce only intermittently locked stitches lesser in number than the number of needle reciprocations of the sewing machine.

It is another object of this invention to provide a novel zig zag sewing machine of the side facing bobbin type in which the oscillating movement of the loop taking mechanism can be selectively controlled to selectively either allow or prevent the formation of locked stitches.

It is still another object of this invention to provide a novel zig zag type sewing machine of the side facing bobbin type in which the oscillating movement of the loop forming mechanism can be selectively prevented so that during zig zag stitching, a lock stitch is formed only when the needle is in one position and not formed when the needle is in the other of the zig zag positions.

According to the present invention, the shifting movement of the bobbin and loop forming mechanism is controlled so as to allow the shuttle hook to be selectively spaced a sufficient distance away from the needle in one mode of operation so that the point of the shuttle hook cannot enter the needle thread loop to cause the needle thread to be interlocked with the bobbin thread with the result that the needle thread loop is pulled back upward through the fabric by the needle and no stitch'is formed. Thus, if the machine is arranged so that normally the shuttle hook is spaced away from the needle so as to prevent stitch formation and then moved into a position adjacent the needle to allow the formation of a single complete stitch at intermittent times such as every sixth to twelfth reciprocation of the needle, 3. locked stitch will be formed having a stitch length equal to six to twelve times the normal stitch length.

According to the preferred embodiment of the present invention a zig zag sewing fachine arranged to automatically sew blind hem stitches, such as a zig zag machine having a needle position control and at least one pattern cam arranged to control the amplitude of the zig zag stitches may be used to produce a basting stitch of the type described above. In the shift drive mechanism for the bobbin and loop forming mechanism a link is employed which may be varied in length to selectively control the position of the shuttle hook between a position adjacent the needle where a locked stitch is formed and a position away from the needle where no stitch is formed. Using a blind stitch zig zag pattern cam the shuttle hook is held away from the needle during the formation of the straight stitches and allowed to move adjacent the needle at the peaks of the blind stitch so that the locked stitch is formed only between the peaks of the blind stitch. Between these peaks or locked stitches the needle thread lies smoothly in a straight line along the top surface of the fabric and likewise the bobbin thread lies in a straight line along the bottom surface of the fabric.

Since lock stitches will be formed only when the needle is on one side of the zig zag movement, with ordinary alternating zig zag movement, a stitch will be formed on every other reciprocation of the needle so that instead of sewing the pattern of varying amplitude determined by the pattern cam, a straight stitch of double the stitch length set in the machine will be formed which will shift laterally of the fabric under straight stitch conditions to form a line of straight stitches having a configuration conforming to the one side edge of the zig zag pattern.

Further details and features of the invention are shown in the accompanying drawings of a preferred embodiment of the invention whose construction and operation are described in the following detailed specification.

In the drawings:

FIGURE 1 is a front elevational view of a sewing machine incorporating the present invention;

FIGURE 2 is a fragmentary perspective view showing the variable length link of the present invention;

FIGURE 3 is a plan view of the link arrangement showing the link in its straightened position;

FIGURE 4 is a plan view of the link arrangement showing the link in its shortened position;

FIGURE 5 is a fragmentary elevational view showing the needle and shuttle hook positioned relative to one another so as to form an interlocked stitch;

FIGURE 6 is a fragmentary elevational view similar to FIGURE 5 but showing the shuttle hook spaced away from the needle to present the shuttle hook from passing through the needle thread loop;

FIGURE 7 is a plan view of a conventional form of the blind hem stitch;

FIGURE 8 is a plan view of the basting stitch formed in accordance with the present invention; and

FIGURE 9 is a cross-sectional elevational view of the stitch of FIGURE 8.

Referring now to the embodiment of the invention shown in the drawings, the sewing machine shown generally in FIGURE 1 includes a bed plate 10 which incorporates the usual cloth feeding mechanism, the feed dogs of which are shown at 11, together with a side facing bobbin and loop forming mechanism indicated generally at 12. At one end of the bed plate 10 is an upstanding hollow column or standard 14 to which is connected a horizontally extending hollow arm 16 terminating in a head portion 18. Extending below the head 18 is a vertically reciprocating needle bar 20 and needle 21 which cooperate with the bobbin and loop forming mechanism 12 to form a completed stitch.

The illustrated sewing machine is of the zig zag stitch type and includes a stitch width selector lever 23, a stitch length selector dial 25 and a needle position selector lever 27. The machine also includes the usual hand wheel 28, bobbin winding mechanism 29 and thread tension selector dial 30 as well as a reverse button 31 and a feed dog height adjusting knob 32.

The needle bar 20 is mounted for reciprocating sliding movement in the usual manner on a needle bar guide 33 which in turn is pivotally mounted at its upper end on the head 13 by a pivot bolt 34 for oscillating movement about a horizontal axis laterally across the bed plate 10 by a connecting link 35. It will be understood that by oscillating the needle bar guide in timed relationship with the cyclic reciprocation of the needle bar 20 and the remainder of the stitch forming mechanism various stitch patterns can be obtained. The present invention is concerned with the mechanism for the transverse shifting of the bobbin and loop forming mechanism 12 and the remaining portions of the complete sewing machine will not be described in further detail. The zig zag mechanism also may be of any conventional type capable of producing patterns in addition to the simple zig zag movement including the blind hem stitch but this mechanism is not part of this invention and will not be described in further detail.

In accordance with the usual sewing machine construction, the bed bed plate 10, column 14, transverse arm 16, and head 18 are preferably formed together as a unit in a casting of a suitable metal such as cast iron or, for purposes of light weight, aluminum. The base plate 10 is relatively thick casting which serves as a frame upon which various mechanisms are mounted.

FIGURES 2, 3, and 4 illustrate the drive mechanism for th oscillating side facing bobbin and shuttle arrangement utilized in the illustrated embodiment of the present invention. The oscillating drive for the shuttle (not shown) of the bobbin and loop forming mechanism 12 includes an oscillating shaft 36 journalled within a pair of bearing bosses 38 and 40 on the underside of the bed plate 10.

In accordance with standard sewing machine construction the oscillating shaft 36 is driven off of the 'main shaft (not shown) through a yoke and sliding block arrangement (not shown) connected to the right end of the shaft 36. The left end of shaft 36 is connected to the bobbin and loop forming mechanism 12 which includes a shuttle housing 42 having a longitudinally extending sleeve 43 slidably disposed within the bearing boss 38 and slidably receiving the oscillating shaft 36 therein. Mounted on the left end of the oscillating shaft within the shuttle housing 42 is a hub 45 carrying the shuttle driver arm 46. The shuttle driver arm 46 drives the shuttle (not shown) within the shuttle race portion 47 of the shuttle housing.

During the normal straight stitch forming operations of the sewing machine, the bobbin and loop forming mechanism 12 are maintained in a fixed position relative to the bearing boss 38. However, during the formation of a zig zag stitch the bobbin and loop forming mechanism 12 are shifted along the longitudinal axis of the shaft 36 relative to the boss 38 in timed relationship to the zig zag movement of the needle 21 to maintain a constant and uniform relative position between the shuttle book 48 (see FIG. 5) and the needle at all lateral positions of the needle. This synchronized longitudinal shifting of the needle 21 and shuttle hook 48 is necessary to assure uniform stitch formation as the shuttle hook passes through a needle thread loop formed between the needle eye and the lower surface of the fabric.

The bobbin and loop forming mechanism 12 is shifted along the longitudinal axis of the oscillating shaft 36 by a link 50 driven in timed relationship to the zig zag movement of the needle 21. The left end of link 50 is pivotally connected at 54 to a collar 55 mounted on the exterior of sleeve 43. A guide pin 56 extending from the boss 38 cooperates with a groove 57 in collar 55 to prevent rotation of sleeve 43 as the bobbin and loop forming mechanism 12 is shifted longitudinally by link 50.

The right end of the link 50 is pivotally connected at 58 to an arm 59 on a rocker shaft 60. One end of rocker shaft 60 is journalled within a lug portion 41 of the bearing boss 40 while the other end is interconnected in any well known manner with the zig zag mechanism which shifts the needle bar 20 from side to side during the formation of a ig zag stitch. Thus, the rocker shaft 60 rocks or oscillates in timed relationship to the zig zag movements of the needle bar 20. The foregoing construction is conventional and well known and in prior art machines the link 50 has been of single piece rigid construction.

In accordance with the present invention, the link 50 is arranged so that under certain circumstances it can vary the distance between the pivoted ends 54 and 58. The link 50 is formed of two sections 51 and 52 of substantially equal length and connected to the pivots 54 and 58 at their outer ends. The sections 51 and 52 are then pivoted to each other at 53 so that the link sections in effect form a toggle which, when in the straight position with the two sections 51 and 52 in line, is of such a length to maintain the loop forming mechanism 12 in the proper position with respect to the needle 21 to form completed stitches with the shuttle hook passing through the needle thread loop in the normal manner. However, if the links 51 and 52 pivot with respect to each other or break the toggle, the distance between the two pivots 54 and 58 will be shortened so that the loop forming mechanism 12 is spaced away from the needle 21 and the needle thread will be drawn back upward through the fabric without passing around the bobbin thread to form a lock stitch.

The arrangement for controlling the breaking or shortening action of the link sections 51 and 52 includes a tension spring 64 extending between a pair of projecting arms 61 and 62 on the link sections 51 and 52, respectively, which operates to tend to keep the sections in alignment so that the link 50 is straight and provides the full length between the pivots 54 and 58. In order to prevent the tension spring 64 from pulling the links over center, the left link 51 has an extension 65 extending beyond the pivot 53, and this extension carries a stop tab 66 adapted to make abutting contact with the side of the link 52 to maintain the links in alignment under the action of the spring 64. In order to provide a positive limit on the breaking action of the links, a bracket 68 is fastened to the arm 52 by a screw 69 and carries a tab 70 which is also engageable by the stop tab 66 in the broken position as shown in FIGURE 4.

The selective operation of the mechanism for allowing braking or shortening of the link 50 is controlled by the feed dog height selector knob 32. This knob is connected to one end of a shaft 72 running through the bed plate and a boss 73. A crank or cam 75 is secured to the bottom end of the shaft 69 below the bed plate 10 and boss 73.'A connecting rod 76 is attached at the one end to the crank 75 and connects to a tapered pin 77 in a conventional feed dog height adjustment assembly 78 so that by rotation of the shaft 69, the tapered pin 77 is moved in and out of the assembly 78 to vary the feed dog height. In a typical sewing machine having three positions, the intermediate or lower position corresponds to the position of the crank 75 in FIGURE 3 and motion to the down and high positions results from a rotation of the crank about 45 in each direction from this position.

In order to actuate the intermittent stitch mechanism of this invention, the shaft 72 and hence cam 75 are rotated beyond the high position an additional 45 to the position shown in FIGURE 4. To prevent unintentional engagement of the intermittent stitch action, rotation of the knob 32 will not normally bring the crank 75 into this position, and a latch 82 (see FIGURE 1) must be actuated to allow the additional rotation of the knob 32 to the position of FIGURE 4.

The crank or cam 75 has a cam surface 80 which rocks a T-shaped lever 84 into a different position when the cam is rotated to the position of FIGURE 4. The lever 84 has a projecting leg 85 intermediate its ends which is pivoted at 86 on the boss 73. A torsion spring 88 is mounted on the pivot 86 and serves to bias the lever 84 in a clockwise direction about the pivot 86 so as to urge the upper arm 89 toward the crank 75. The upper arm 89 has a cam follower tab 91 which makes contact with the periphery of the crank or cam 75 which when rotated so that the cam surface is in the position of FIGURE 4 serves to rotate the lever 84 in a counterclockwise direction against the biasing force of the torsion spring 88.

When the lever 84 is rotated to the position of FIG- URE 4, the lower arm 93, which carries a roller 94 attached eccentrically to the arm 93 by screw 95 for adjustment purposes, is shifted toward the right. In this position, a projecting arm 97 on the right hand link 52 is positioned to engage the roller 94 whenever the rocker shaft arm 59 tends to shift the loop forming mechanism toward the left hand needle position.

The operation of this can best be understood by noting that in both FIGURES 3 and 4 the rocker shaft arm 59 has shifted to move the loop forming mechanism toward the left hand position. In this case, when the intermittent stitch mechanism is not operated, the arm 97 does not make contact with the roller 94 and therefore the link 50 remains in the straight position at all times and the bobbin case shifts with the needle to form lock stitches at all times. However, when the lever 84 is rotated to shift the roller 94 to the position of FIGURE 4 the arm 97 will still remain out of contact with the roller 94 when the rocker shaft arm 59 is shifted to the right hand needle position. However, as the arm 59 shifts toward the left needle position, the arm 97 comes into abutting contact with the roller 94 which is fixed in position because of the engagement of the follower tab 91 with the cam lobe 80. Since this force is applied away from the pivot 58, it tends to rock the link 52 in a clockwise direction to break the toggle against the force of the spring 64. Since this effectively shortens the distance between the pivots 54 and 58, the loop forming mechanism does not shift all the way to the left needle position but remains spaced away a sufiicient distance that the shuttle hook is unable to pass through the needle thread loop and no stitch is formed.

The relative positions of the needle and the shuttle hook are shown in FIGURES 5 and 6. Under normal conditions where a lock stitch is formed, the shuttle hook 48 is positioned as shown in FIGURE 5 to pass very close to the needle 21. As the needle passes through the cloth 99 and on its reversal upward, the thread is held within the fabric 99 and the upward movement of the needle causes a loop 101 to appear between the needle eye 22 and the fabric 99. The loop forming mechanism 12 is driven in such timed relationship as to cause the tip 49 of the shuttle hook 48 to pass through and engage the thread loop 101 as it reaches its maximum dimension,

and this causes the loop to be enlarged to pass around the shuttle and bobbin to form a lock stitch.

However, when the loop forming mechanism 12 is not shifted toward the left in the previously described manner and the needle is in the left position while the loop forming mechanism remains in the right hand position, the parts assume the relationship shown in FIGURE 6. It will be seen that the shuttle hook 48 is now spaced away from the needle 21 such a distance that the shuttle hook tip 49 is unable to pass within the thread loop 101. In such case, the shuttle hook 48 continues to move without engaging the thread which is then pulled back upward through the fabric without forming a lock stitch and without having any portion of the needle thread remain below the upper surface of the fabric. Thus, after a succession of such stitches, the appearance of the fabric may indicate the individual holes formed by the needle passing through the fabric but the needle thread lies along the upper surface of the fabric and the bobbin thread lies along the lower surface of the fabric.

FIGURES 7, 8, and 9 illustrate how a basting stitch is obtained while the zig zag mechanism follows the pattern for a blind hem stitch. FIGURE 7 illustrates a typical blind hem stitch sewn by a machine in which the link 50 remains rigid so that lock stitches are formed on every reciprocation of the needle. With this arrangement, lock stitches are for-med which may be six or more in number with the needle remaining in the left hand needle position. These stitches as shown at 103 are normal straight stitches such as would be formed on a straight stitch machine. However, in forming the blind hem stitch, at regular intervals one stitch is formed in the right needle position as shown at 104. The zig zag mechan1sm 1s arranged so that after sewing the last of the stitches in the left position the needle is moved toward the right position for one stitch and then moved back to the left position for the next series of stitches. This results in an alternating arrangement of a series of straight stitches in the left position interrupted at regular intervals by a single stitch in the right needle position.

However, when mechanism of the present invention is brought into operation by rotating the crank 76 to the position of FIGURE 4, the loop forming mechanism 12 is unable to shift far enough to form lock stitches in the left needle position and the resulting stitch appears as in FIGURES 8 and 9. These show the present invention in operation with the same stitch length as determined by the stroke of the feed dogs and the same cam action as in FIGURE 7. However, there are merely a number of holes in the fabric without any lock stitches formed in the left needle position and a stitch is formed only when the needle is shifted to the right position giving an extremely long spacing between the stitches 106. Thus, as shown in FIGURE 9, the tension on the needle thread 107 and bobbin thread 108 causes them to shift over from the left position to lie on a line in the right position between the stitches 106 smoothly along the top and bottom surfaces of the fabrc 99. It should be pointed out that in order to allow very easy removal of the stitch, the needle thread tensioning mechanism 30 should be set for maximum tension so as to pull the bobbin thread upward through the cloth and form an unbalanced lock stitch so that the needle thread can more easily be removed by simple tension. To provide the extra tension required, it may be necessary to wrap the needle thread around the needle for one full turn, depending upon the nature of thefabric.

If other patterns than the blind hem stitch pattern are used, the operation of this invention by turning the crank to the position of FIGURE 4 will still result in a stitch formation only when the needle moves into the right hand position. In such case, when various patterns are used, instead of forming zig zag stitches which give the full width of the pattern, a straight line stitch will be formed between the right needle position portions so that the resultant stitch follows the right hand outline of the pattern rather than forming zig zag stitches between the two needle positions. Thus, the use of this invention increases the versatility of a zig zag sewing machine by providing decorative stitch patterns in addition to those obtainable by the'normal zig zag movement.

While the preferred embodiment of this invention has been shown and described in detail, it is recognized that upon a complete understanding of this invention, various modificatons and rearrangements will readily occur to those skilled in the art and may be resorted to without departing from the scope of the invention.

I claim:

1. A sewing machine having a frame including a bed plate and a head structure above the bed plate, a needle bar guide mounted on said head for lateral swinging movement between left and right needle positions, a needle carried by said needle bar guide for vertical reciprocating movement to and from said bed plate, a loop forming mechanism on said sewing machine below said bed plate, said loop forming mechanism including a shuttle and a bobbin, a needle thread carried by said needle and a bobbin thread carried by said bobbin whereby rotary movement of said shuttle interlocks said needle thread and bobbin thread to form lock stitches, wherein the improvement comprises control means operable to move said shuttle relative to said needle in at least one of said needle positions, whereby said shuttle is movable to one position to cause said shuttle to engage said needle thread to form a lock stitch and said shuttle is movable to another position where said shuttle does not engage said needle thread and no lock stitch is formed.

2. A sewing machine as set forth in claim 1 wherein said control means includes linkage means operable to shift said shuttle relative to said needle and selectively operable means to vary the effective length of said linkage means.

3. A sewing machine having a frame including a bed plate and a head structure above the bed plate, a needle bar guide mounted in said head for lateral swinging movement between left and right needle positions, a needle carried by said needle bar guide for vertical reciprocating movement to and from said bed plate, a loop forming mechanism on said sewing machine below said bed plate, said loop forming mechanism including a bobbin and a side facing shuttle rotatable about an axis substantially parallel to the plane of the swinging movement of said needle bar guide, said loop forming mechanism being mounted for horizontal movement along said axis, linkage means operable responsive to the zig zag movement of said needle bar guide to shift said loop forming mechanism in timed relationship therewth, a needle thread carried by said bobbin, whereby rotary movement of the shuttle interlocks said needle thread and bobbin thread to form locked stitches, control means operable to the move said shuttle along said axis whereby said shuttle is positioned to form locked stitchesin said right needle position, and is selectively spaced away from said needle in said left needle position whereby said shuttle does not engage said needle thread and no locked stitch is formed at said left needle position.

4. A sewing machine as set forth in claim 3 wherein said linkage for shifting said loop forming mechanism can be changed in length and said control means operates t change said linkage length when said needle bar guide is in said left position so that said shuttle remains at said right needle position.

5. A sewing machine as set forth in claim 4 wherein said variable length link comprises two links pivoted together to form a toggle, whereb when said links are straight said loop forming mechanism can be shifted to said left needle position and when said links assume an angular position, said loop forming mechanism remains in the right needle position.

6. A sewing machine having a frame including a bed plate and a head structure above the bed plate, a needle bar guide mounted on said head for lateral swinging movement between left and right needle positions, a needle carried by said needle bar guide for vertical reciprocating movement to and from said bed plate, zig zag mechanism constructed and arranged to shift said needle bar guide between said left and right needle positions, a loop forming mechanism on said sewing machine below said bed plate, said loop forming mechanism including a side facing shuttle mounted for rotation about a horizontal axis substantially parallel to said bed plate, said loop forming mechanism being shiftable along said axis, drive mechanism operable responsive to said zig zag mechanism to shift said loop forming mechanism in timed relationship to the movement of said needle bar guide, said drive mechanism including a rock shaft having an end extending below said bed plate and linkage means interconnecting said rock shaft and said loop forming mechanism, and control means selectively operable to change the length of said linkage means whereby when said control means is inoperable, said linkage means shifts said loop forming mechanism with said needle bar guide to maintain a relative position between said shuttle and said needle to form locked stitches and when said control means is operable, said linkage means changes in length responsive to movement of said rock shaft to maintain said loop forming mechanism at said right needle position whereby said shuttle is positioned adjacent said needle at said right needle position to form locked stitches and said shuttle is spaced away from said needle at said left needle position to prevent the formation of locked stitches.

7. A sewing machine as set forth in claim 6 wherein said variable length linkage means includes first and second links operably connected to each other and connected to said loop forming mechanism and said rock shaft to form a toggle link whereby when said links are in alignment when said control means is inoperative said loop forming mechanism is shifted between said left and right needle positions and when said control means is operative, said links assume an angular relationship when said rock shaft tends to shift said loop forming mechanism toward said left needle position so that said 100p forming mechanism remains at said right needle position when said needle is shifted to said left needle position.

8. A sewing machine as set forth in claim 7 wherein one of said links has a projecting arm and said control means positions a stop engageable by said arm to break said toggle to maintain said loop forming mechanism at said right needle position.

References Cited UNITED STATES PATENTS 1,411,003 3/1922 DeVoe 112--l54 XR 3,361,100 1/1968 Bono 1l2159 3,384,042 5/1968 Gianinazzi 1l2158 RICHARD J. SCANLAN, JR., Primary Examiner 

